1. Field of the Invention
The present invention relates to lubricating oils for use in internal combustion engines which increase the fuel economy of said engines.
2. Description of the Related Art
In recent years great emphasis has been placed by engine manufacturers in increasing the fuel economy and efficiency of their engines in order to meet the Federal Corporate Average Fuel Economy (CAFE) standards. While a significant portion of such improvement has and will be achieved by improvements in engine design and operation, a major role can be played by the lubricants used in said engines. Lubricants finction to reduce and disperse engine deposits which accumulate when the engines are running. They also serve to reduce the friction between moving parts which are in metal surface to metal surface contact.
Numerous additives have been introduced into lubricating oils to enhance the ability of base oils to disperse contaminants, resist oxidation, reduce frictional losses and serve as metal deactivators, extreme pressure additives, viscometric property improvers, rust inhibitors, anti-foaming agent, detergents and so forth.
U.S. Pat. No. 5,114,602 is directed to lube oils containing borated succinimide ashless dispersants which also show a reduced tendency to degrade engine seals.
U.S. Pat. No. 5,356,547 is directed to a lube oil having a low coefficient of friction and reduced copper corrosivity containing at least one organomolybdenum compound selected from the group consisting of sulfirized oxymolybdenum dithiocarbamate and sulfurized oxymolybdenum organophosphororodithioate phosphorodithioate as friction modifiers, and at least one organozinc compound selected from the group consisting of zinc dithiophosphate and zinc dithiocarbamate as extreme pressure, anti-oxidant and corrosion inhibiting agents, and an organic acid amide which serves to reduce the coefficient of friction at an early stage of engine running after startup while inhibiting copper corrosion.
U.S. Pat. No. 4,801,390 is directed to a lubricating oil composition containing an ashless dispersant which is a polyisobutylene succinic anhydride reacted with a polyethylene amine and subsequently treated with a boron compound.
EP 562172 is directed to an engine oil composition containing a natural or synthetic base oil stock, a boron compound derivative of an alkenylsuccinimide, an alkaline earth metal salt of salicylic acid and one or both of a molybdenum dithiophosphate and molybdenum dithiocarbamate. The lube oil formulation may also contain viscosity index improvers such as polymethacrylate, polyisobutylene, ethylene-propylene copolymers, etc., pour point depressants such as polyalkylmethacrylates, antioxidants such as hindered phenolic compounds and dispersant/detergents such as sulfonates, phenates and the like.
It would be desirable to improve the fuel economy properties of engine oils substantially containing the currently industry accepted additives.